6/4 POPULAR SCIENCE MONTHLY. 



the aid of the balance the plienomena of combustion were rendered 

 intelligible. The foundations of chemistry were laid, and upon 

 them the nineteenth centuiy has built. Lavoisier, the greatest of 

 the founders, fell a victim to the guillotine; the judge who con- 

 demned him refused all appeals for mercy, saying " the republic 

 has no need for savants," but the necessity which judicial ignorance 

 could not foresee presently made itself felt. France, at war with 

 all Europe, her ports closed to supplies from without, fell back 

 upon her own resources. Saltpeter was needed for her guns, alkali 

 for her industries, and the chemist was called upon for help. The 

 stress of continued warfare stimulated intellectual activity, and 

 one result was the creation of chemical processes which revolution- 

 ized more than one industry. The dependence of modern civiliza- 

 tion upon science then began to be recognized — a dependence which 

 is, perhaps, the chief characteristic of the present century. 



With the opening of the new century a period of great activity 

 began. The constancy of matter was well established, and the 

 fundamental distinction between elements and compounds was 

 clearly recognized; two starting points for exact research had been 

 gained. Only a small number of elements, however, had been 

 identified as such; of some substances it was doubtful whether they 

 were elementary or not, but the mine was open and a rich body of 

 ore was in sight. Furthermore, the utility of research had become 

 evident, so that intellectual curiosity received a new stimulus and 

 a new direction. Theory and practice became partners, and have 

 worked together to this day. 



Between the years 1803 and 1808 one of the greatest advances 

 in scientific chemistry was made, when John Dalton announced and 

 developed his famous atomic theory. In this we find a notable 

 illustration of the difference between metaphysics and science. 

 The conception of matter as made up of atoms, as discrete rather 

 than continuous, was a commonplace of philosophical speculation. 

 It had been taught by Democritus and Lucretius; it was the theme 

 of wordy wrangles during centuries; Swedenborg, Higgins, and 

 other writers had sought to apply it to the discussion of chemical 

 phenomena; but it remained only a speculation, unfruitful for dis- 

 covery. Up to the time of Dalton it had led to nothing but intel- 

 lectual gymnastics. 



A good scientific theory is never a product of the unaided 

 imagination; it must serve some purpose in the correlation of phe- 

 nomena which suggest it to the mind. This was the case with 

 Dalton's discovery, which grew out of his observations upon definite 

 and multiple proportions. That every chemical compound has a 

 fixed and definite composition was recognized by Lavoisier, and by 



